Open hearth furnace



Patented June 30, 1936 PATENT oTFicE" OPEN HEARTH FURNACE Karl von der Lahr, Dusseldorf, Germany No Drawing. Application.April 10, 1935, Serial No. 15,519 /2. In Germany July 23, 1934 2 Claims. (01. 263-52) This invention relates to a process of improving the melting effect in open hearth furnaces heated with fuel gases.

It has been found that in heating open hearth 5 furnaces with purified coke oven gas or similar fuel gases the slightly luminous flame produced thereby caused a reduction of the heating value while the complete extraction of the tar, which is important particularly for long distance gas supply plants, involved a prolonged charging time and thus led to considerable losses. To remove this drawback it was attempted to carburize the gas by adding thereto tar, oil or benzene in the form of fine sprays so as to form a bright flame and thus insure a better transmission of heat to the charge or bath. However, this method of increasing the efficiency of the gas flame requires at least a percent addition of a carburizing agent, causes frequent troubles and is expensive, owing to the high prices of these agents. It is further known to employ blast air or steam for supplying and carburizing these agents. Fuel gas, in most cases purified coke oven gas, is supplied to the nozzles at a pressure 2 of about 300 mm. of water column, whereas the carrying and atomizing air of the carburizing agents possesses greater pressure in order to carry the latter, which are protected by their surrounding gas core, as quickly as possible and in good condition into the combustion space. The hot air rising in the ducts of open hearth furnaces has generally a temperature of 1000 1250" C. If the combustible dust were blown in with air from the gas nozzle in the core of 35 the gas current, ignition with the supporting air would take place owing to the heating of the surrounding masonry by radiation, as observed in connection with all known carburizing agents. Owing to the increase in volume of the 40 core, this ignition causes a considerable braking effect within the main gas current coming out of the nozzles, which covers the entire current, so that even at the circumference of the latter combustion at an increased rate is effected also with the aid of the hot air rising from the air duct.

Aside from the fact that these previous combustion processes in the furnace head bring about unintended considerable overheating and take away a part of the carburizing agent already in the head without regard for the real purpose of. the process, this braking of the kinetic energy has a very unfavorable influence upon the action of the flame on the charge in the hearth or upon the bath itself, so that a very large part of the dust residue is not thrown into the furnace charge or into the melting bath but carried into the furnace chamber by the flame draft. As this dust will stick to the hot packing of the regenerators, considerable destruction of'the brickwork is unavoidable. If steam is used as atomizing agent the'carburizing agent will also be ignited by the oxygen released during the decomposition of the steam.

The invention eliminates the drawbacks mentioned and. at the same time attains greater economy by adding to the coke oven or fuel gas combustible dust, e. g., coal dust, as carburizing agent. Furthermore, the carburizing agent is supplied and atomized by means of compressed and purified fuel gas, and the carrier of the carburizing dust is supplied at greater pressure and at considerably higher speed than the fuel gas used for the operation of the furnace.

The new process saves not only costs, but attains also special advantages. The combustible dust blown in consists preferably of a substance that is free from ashes to produce a strongly radiating flame, so that rapid melting of the scrap metal is insured on account of better heat development and shorter charging periods. By correspondingly adjusting the spray nozzles for the combustible coal dust, the jet of the latter may be directed to the melting zone of the furnace for the purpose of covering the material to be melted with a film of combustible coal dust, by which the material is protected against oxidation, atmospheric oxygen being thus excluded from coming in contact with the said material. Better heating results in better reactivity of the slag, and very little material is therefore lost through the latter. The furnace is protected against overheating, as the bath remains heat absorbent due to the better working of the slag, and this involves a considerable saving in refractory material and repair costs.

To prevent premature combustion of gas and dust and the resulting braking 0f the kinetic energy of the gas current, the dust is preferably blown in by compressed gas. This simple expedient renders premature burning of the blowing medium in the surrounding main gas current impossible. The main gas current protects perfectly the carburizing agent blown into the core and, owing to the unimpaired kinetic energy, carries it into the melting space wherein the non-combustible residual constituents are separated also.

I claim:-

1. A process for improving the'melting efi'ect the centre or core of the main -gas current a 'carburi'zing agent in pulverized form' and introducing said carburizing agent at a higher velocity than the main gas current for operating the furnace.

10 2. A process for improving the melting process 7 tion.' 7

in open hearth furnaces heated with cold purified coke oven gas or purified producer gas, consisting in introducing into and directing through the centre or core of the main gas, current, a carburizing'agent in pulverized form and introducing said carburizing agentby means of'a jet of jurified gas and at" higher velocity than the main gas current intended for furnace opera- KARL v. n. LAHR. 1o 

